Understanding Disaster Risk on Volcanic Islands: a research agenda

April 11-13, 200

A trapped mercury 199 ion frequency standard

Mercury 199 ions confined in an RF quadrupole trap and optically pumped by mercury 202 ion resonance light are investigated as the basis for a high performance frequency standard with commercial possibilities. Results achieved and estimates of the potential performance of such a standard are given

Many Body Problems with "Spin"-Related Contact Interactions

We study quantum mechanical systems with "spin"-related contact interactions in one dimension. The boundary conditions describing the contact interactions are dependent on the spin states of the particles. In particular we investigate the integrability of $N$-body systems with $\delta$-interactions and point spin couplings. Bethe ansatz solutions, bound states and scattering matrices are explicitly given. The cases of generalized separated boundary condition and some Hamiltonian operators corresponding to special spin related boundary conditions are also discussed.Comment: 13 pages, Late

Thermoelectric properties of Co, Ir, and Os-Doped FeSi Alloys: Evidence for Strong Electron-Phonon Coupling

The effects of various transition metal dopants on the electrical and thermal transport properties of Fe1-xMxSi alloys (M= Co, Ir, Os) are reported. The maximum thermoelectric figure of merit ZTmax is improved from 0.007 at 60 K for pure FeSi to ZT = 0.08 at 100 K for 4% Ir doping. A comparison of the thermal conductivity data among Os, Ir and Co doped alloys indicates strong electron-phonon coupling in this compound. Because of this interaction, the common approximation of dividing the total thermal conductivity into independent electronic and lattice components ({\kappa}Total = {\kappa}electronic + {\kappa}lattice) fails for these alloys. The effects of grain size on thermoelectric properties of Fe0.96Ir0.04Si alloys are also reported. The thermal conductivity can be lowered by about 50% with little or no effect on the electrical resistivity or Seebeck coefficient. This results in ZTmax = 0.125 at 100 K, still about a factor of five too low for solid-state refrigeration applications

Time Ordering in Kicked Qubits

We examine time ordering effects in strongly, suddenly perturbed two-state quantum systems (kicked qubits) by comparing results with time ordering to results without time ordering. Simple analytic expressions are given for state occupation amplitudes and probabilities for singly and multiply kicked qubits. We investigate the limit of no time ordering, which can differ in different representations.Comment: 26 pages, 5 figure

Lunar particle shadows and boundary layer experiment: Plasma and energetic particles on the Apollo 15 and 16 subsatellites

The lunar particle shadows and boundary layer experiments aboard the Apollo 15 and 16 subsatellites and scientific reduction and analysis of the data to date are discussed with emphasis on four major topics: solar particles; interplanetry particle phenomena; lunar interactions; and topology and dynamics of the magnetosphere at lunar orbit. The studies of solar and interplanetary particles concentrated on the low energy region which was essentially unexplored, and the studies of lunar interaction pointed up the transition from single particle to plasma characteristics. The analysis concentrated on the electron angular distributions as highly sensitive indicators of localized magnetization of the lunar surface. Magnetosphere experiments provided the first electric field measurements in the distant magnetotail, as well as comprehensive low energy particle measurements at lunar distance

Four-well tunneling states and elastic response of clathrates

We present resonant ultrasound elastic constant measurements of the clathrate compounds Eu8Ga16Ge30 and Sr8Ga16Ge30. The elastic response of the Eu clathrate provides clear evidence for the existence of a new type of four-well tunneling states, described by two nearly degenerate four level systems (FLS). The FLS's are closely linked with the fourfold split positions of Eu known from neutron diffraction density profiles. Using a realistic potential we estimate the tunneling frequencies and show that the energy gap between the two FLS's is of the same order as the Einstein oscillator frequency. This explains why the observed harmonic oscillator type specific heat is not modified by tunneling states. In addition the quadrupolar interaction of FLS's with elastic strains explains the pronounced depression observed in elastic constant measurements. In the case of the Sr clathrate, we show that the shallow dip in the elastic constant c44 is explained using the same type of quadrupolar interaction with a soft Einstein mode instead of a FLS.Comment: 4 pages, 4 figures; accepted for publication in Physical Review Letter

Dephasing Effects by Ferromagnetic Boundary on Resistivity in Disordered Metallic Layer

The resistivity of disordered metallic layer sandwiched by two ferromagnetic layers at low-temperature is investigated theoretically. It is shown that the magnetic field acting at the interface does not affect the classical Boltzmann resistivity but causes a dephasing among electrons in the presence of the spin-orbit interaction, suppressing the anti-localization due to the spin-orbit interaction. The dephasing turns out to be stronger in the case where the magnetization of the two layers is parallel, contributing to a positive magnetoresistance close to a switching field at low temperature.Comment: 11 pages, 3 figures. Title modified in journal versio